Fluoroelastomers and in particular perfluoroelastomers such as those described in “Modern Fluoropolymers”, edited by John Scheirs, Wiley Science 1997, offer excellent protection against high service temperatures and are resistant to a wide variety of chemical reagents. Because they have excellent heat resistance and oil resistance, fluoroelastomers have been used in the past for O-rings, gaskets, oil seals, diaphragms, hoses, rolls, sheeting materials, in a variety of industrial applications which include automobiles, boats, aircraft, hydraulic machinery, general machinery, and in fields related to prevention of pollution. In the automotive field, the heat resistance and oil resistance of fluoroelastomers are commonly utilised in fuel management systems. Parts of the fuel management systems in which fluoroelastomers are often used include fuel tanks, fuel hoses, in-tank hoses and filler hoses.
Fluoroelastomers are typically obtained by curing a generally amorphous fluoropolymer. Two main systems are known today to effect curing of fluoropolymers, i.e. polymers that have a partially or fully fluorinated backbone. One cure system is based on the use of a polyhydroxy compound generally in combination with an onium compound. The second well known cure system is based on a peroxide cure reaction and requires besides the presence of an organic peroxide also the presence of special cure sites in the fluoropolymer which makes the fluoroelastomers obtained with a peroxide cure system generally more expensive than a cure system based on polyhydroxy compounds. These special cure sites comprise bromine and/or iodine which is capable of participating in the organic peroxide cure reaction. It is generally believed that such bromine or iodine atoms are abstracted in the free radical peroxide cure reaction, thereby causing in the presence of coagents, the fluoropolymer molecules being linked together to a three dimensional network. Chlorine is generally not capable of being abstracted in such a reaction and has so far not been used as a cure site for a peroxide cure system.
For example, EP 761735 describes curable fluoroelastomer compositions that require the presence of bromine in the fluoropolymer in order to obtain a peroxide curable system. In particular, EP 761735 teaches that the cure reaction involving homolytic scission of C—Br bonds can be accelerated by using certain metalorganic hydrides. EP 761735 does not appreciate the possibility of using chlorine as a cure site.
A disadvantage of the so called peroxide cure systems is that they require the presence of bromine or iodine in the fluoropolymer which leads to inconveniences in the manufacturing of such fluoropolymer and generally increases costs of such fluoropolymers. On the other hand, polyhydroxy cure systems do not require the presence of bromine or iodine but suffer from the disadvantage that some of the physical properties and thermal properties of the resulting fluoroelastomer may be inferior to those of the peroxide cure system.
It would now be desirable to find a further cure system for curing fluoropolymers and to make fluoroelastomers. Desirably, such a cure system would allow producing fluoroelastomers in a convenient and cost effective way. Desirably, the fluoroelastomers produced with the new cure system have similar or improved physical and mechanical properties as fluoroelastomers produced with cure systems of the prior art in particular compared with fluoroelastomers obtained with the known peroxide cure system.